Compartmental ligands

Compartmental ligands routes to homo- and hetero-dinuclear complexes. U. Castellato, P. A. Vigato, D, E. Fenton andM. Vidali, Chem. Soc. Rev., 1979, 8,199-220 (62). 

Unsymmetric compartmental ligands that allow for the controlled synthesis of unsymmetric Ni2 or heterobimetallic NiM complexes have received particular attention.1876,1892 A wide range of such ligands derived particularly from 2-hydroxy-3-hydroxymethyl-5-methylbenzaldehyde and 2-hydroxy-3-hydroxymethyl-bromo-benzaldehyde has now been prepared and used for Ni com-plexation. These ligands have monopodal iminic pendent arms and either mono- or dipodal aminic pendent arms and the terminal donors of the pendent arms can be provided by pyridine, imidazole, and tertiary amino groups.1893-1897 Complexes are usually prepared by reaction of the requisite Ni11 salts with the preformed ligand. 

Macrocyclic Schiff base compartmental ligands (750) (Robson-type ligands) derived from the [2 + 2] condensation of a 2,6-diformyl- or 2,6-diketo-substituted phenol and a diamine are very prominent in dinuclear Ni coordination chemistry.1901-1903 Particular interest lies in magnetic exchange interactions between the adjacent metal ions as well as in bioinorganic chemistry, where such dinuclear complexes have been proposed as synthetic analogues for bimetallosites. 

In order to provide a dinucleating scaffold for proper orientation of two proximite Ni11 ions, compartmental ligands based on bridging alkoxide, phenolate, pyrazolate, or phtalazine units have been employed.422,2066-2082 Selected examples are discussed below. 

Two dinuclear complexes, with five-coordinate zinc centers, derived from tris((2-pyridyl)-methyl) amine were synthesized and bridging phosphate or phosphate ester groups. The X-ray structure of the phosphate monoester complex shows a syn-anti bridging mode in contrast to alkaline phosphatase in which it is syn-syn 448 Fenton and co-workers have also studied other related dizinc species of compartmental ligands 449... 

Triply bridging carbonates between three zinc centers have been identified in nine different X-ray structures deposited in the CSD 458,461,465-467 For example, a binuclear ft-OH zinc complex with a tetradentate /V-donor ligand absorbs atmospheric carbon dioxide to a triply bridged carbonate.468 Examples are also known where the metal atoms are in varying coordination environments. The complex cation [Zn3(bipyridine)6(/U3-C03)(H20)2]4+ contains one penta- and two hexacoordinate zinc centers.469 A tetrapodal compartmental ligand forms a tetrameric complex with zinc that contains the carbonate bridging between three of the four zinc centers.470... 

Heterobinuclear complexes containing alkali or alkaline earth metal cations have been derived from mononuclear transition metal complexes of compartmental ligands (51).288 The molar conductivities of the (51)-CuLi2 series suggest that the complexes are uniunivalent electrolytes in water and so are present in solution as Li[(51b)CuLi]- H20 the corresponding di-sodium, -potassium or -cesium complexes are unibivalent electrolytes and so likely to be present in solution as M2[(51)Cu]- H20. 

A V02+ complex with the compartmental ligand (177) was obtained by the dropwise addition of a VOSO4 solution to an aqueous acetone solution containing LiOH and the ligand.903 The complex is monomeric and the coordination involves the four O atoms. With Ni2+ and Cu2+ both mononuclear positional isomers N202 and 0202 may be prepared according to conditions, but with V02+ only the 0202 positional isomer is obtained. 

A number of the above complexes may be alternatively considered as macrocyclic ligands or compartmental ligands, but as the emphasis has been primarily in terms of the local copper(I) stereochemistry and the polynuclear nature of the complexes, they have been included above. As there is no crystallographic data on biological copper(I) systems, this section will have to await the further refinement of the structure of Panutirus Interruptus hemocyanin.353... 

Acyclic Schiff base derivatives represent a resourceful class of compartmental ligands which are prepared by self-condensation of appropriate formyl and amine precursors. The condensation reaction is simple and generally leads to the desired product in high yield. Literature data on Lnm mono- and bimetallic complexes, as well as on 4f-d transition metal bimetallic entities with these derivatives are abundant and have been reviewed recently (Vigato and Tamburini, 2004). Extension to multimetallic systems and to complexes with 5f elements... 

Lanthanide chemistry with Schiff bases is quite extensive and numerous acyclic, cyclic, monometallic and polymetallic (4f-4f, 4f-5f, 4f-nd) complexes have been synthesized and studied, in particular with compartmental ligands, owing to the ability of the latter to bind two or more metal ions in close proximity. Asymmetrization of these ligands also provides important diversification of the coordinating sites (Vigato and Tamburini, 2004). On the other... 

A broad application of phenolic Sehiff base ligands lies in the synthesis of heterobimetallic complexes. Extended functionalization of the L2 - ligand affords the so-called compartmental ligands which ensure rich coordination chemistry by accomodation of several metals [89, 146]. Some representative ligands are depicted in Fig. 25. 

These and similar polyketones can give rise to compartmental ligands and link two (11-XXXIII) or more (11-XXXIV) metal centers that can then undergo redox reactions. 

The occurrence of manifold bimetallic (and multimetallic) protein active sites has greatly inspired coordination chemists to develop compartmental ligand scaffolds that preorganize two (or even more) metal ions in close proximity, predestined for cooperative reactivity (48-53). While the biological metal ion... 

A series of phenol-based compartmental ligands of types A-C was studied thoroughly as frameworks for dinickel(II) complexes by the groups of Okawa,... 

Compartmental ligands (16) are macrocyclic ligands (as well as nonmacrocyclic ligands) which contain compartments for housing more than one metal ion. Only the macrocyclic counterparts will be treated here. 

Compartmental ligands (16) are derived from diketonates and triketonates and are usually synthesized from Schiff base reactions of the ketone with a diamine. ... 

Compartmental ligands (16) provide extensive opportunities for multiple metal ion complexation. An example of a mixed donor ligand incorporating different metal ions is the macrocyclic trinucleating hgand (63), which is capable of complexing two soft donor metal centers in addition to a hard alkali or alkaline earth metal. ... 

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